1. Field of the Invention
The present invention relates to a graphic display control apparatus for displaying a plurality of component figures respectively corresponding to a plurality of components in a two-dimensional form, by overlapping these component figures with each other in a computer aided design (hereinafter abbreviated to CAD) system.
To be more specific, the present invention relates to a graphic display control apparatus having an ability to overlap a plurality of component figures with each other and display the same on a screen so as to edit figures by utilizing a two-dimensional CAD system, or more particularly, to modify the shape of each of the component figures consisting of gears and the like which are situated overlaid with other, or to change the relationship concerning the location of each of the component figures.
2. Description of the Related Art
In general, for editing component figures using a two-dimensional CAD system, when a function of automatic hidden-line elimination is unavailable, if lines defining frames of a plurality of component figures are overlapped with each other and displayed on a screen of a cathode-ray tube (CRT) or the like, all the lines defining the frames of the component figures residing at the lower level locations are all seen transparently. This causes a drawback that it becomes difficult to grasp the relationships concerning the height direction (i.e., vertical direction) among a plurality of components.
To cope with this drawback, in a conventional graphic display control apparatus, the function of automatic hidden-line elimination is implemented in a two-dimensional CAD system. Respective component figures are painted uniformly so that each of the lines defining the component figures residing at the lower level locations cannot be seen transparently.
When this kind of function of automatic hidden-line elimination is used to edit component figures, it becomes easier to grasp the relationship concerning the height direction among a plurality of components on a screen of a CRT or the like. Consequently, modifying the shape of each of plural component figures or changing the relationship concerning the location among component figures can presumably be achieved efficiently.
However, in a graphic display control apparatus utilizing the foregoing CAD system including the function of automatic hidden-line elimination, when an attempt is made to modify the shape of each of some components or the relationship concerning the location among some components in an assembly drawing produced by combining numerous components, there arises a problem that it is difficult to manipulate components that should be modified, on a screen, because of a hindrance caused by components other than the components that should be modified.
In particular, when component figures of components residing at the higher level locations are larger than component figures of components residing at the lower level locations, since the components at the lower level locations cannot be seen transparently, these components are hidden behind the components at the higher level locations and are therefore not displayed. If a designer or the like attempts to edit the component figures at the lower level locations, these component figures cannot be seen on a screen.